This invention relates generally to the beneficial treatment of organics-contaminated water, and more specifically relates to method and apparatus for remediating groundwater which has become contaminated with hydrocarbons.
Groundwater contamination, typically arising from petroleum storage tank spills or from intentional or accidental discharge of liquid hydrocarbons or compositions containing same, has become a problem of increasing concern in virtually all areas of the world where human activities occur. Aside from contamination of this type which results from industrial complexes, it has unfortunately been found that even suburban neighborhoods which would appear to be havens from such phenomena, have increasingly been found to the consternation of the residents to harbor pools of hydrocarbon pollutants, the source of which is very commonly automobile service station sites at which antiquated or abandoned storage tanks have released gasoline, fuel oils, lubricants and the like into the local groundwater. Other common sources of such noxious material can include dry cleaning establishments and/or manufacturers or distributors of the tetrachloroethane which is used in dry cleaning. Other well-known hazardous hydrocarbon materials include polychlorinated phenols (e.g. PCB's), pentachlorophenols (PCP's), and various aliphatic and aromatic hydrocarbons, as for example gasoline, benzene, naphthalene and various petroleum and petroleum derivative products. Certain particularly pernicious compounds of this type are often considered under the grouping "BTEX", which is understood by those familiar with the art to refer to benzene, toluene, ethyl benzene and the xylenes (m-, p-, and o-). The BTEX content of groundwater or other contaminated sites is frequently regarded as a principle measure of the acceptability of the water in question for human consumption and use and other purposes.
Various remediation techniques have been utilized in the past for treatment of groundwater which has been thus contaminated. Among the most predominate type of systems in present use are those based on so-called "pump and treat" technology. In this method the contaminated groundwater and possibly a phase-separated product is withdrawn from a recovery well sunk into the groundwater and pumped to an above ground treatment facility. Various treatment techniques are thereupon used, such as diffused air treatment and air stripping. Inline filters can also be used; and similarly carbon adsorption can serve to remove contaminants from the displaced groundwater. Systems of the pump and treat type are considered expensive to install and operate. In many instances they basically result in separation or adsorption of the contaminants, and while purified water may result from the treatment, the problem often remains of disposing of the contaminants which have thus been separated.
In recent years increasing interest has also been evidenced in bioremediation technology. The technology has been of great interest, but its effective use in treating groundwater has been limited. The procedures are very complex, involving the use of expensive and complex reactors, and can cause adverse geochemical reactions, and can even introduce new toxic compounds beyond those which are being treated.
Pursuant to the foregoing, techniques have been sought which would serve to directly treat the contaminated groundwater in both effective and economical fashion.
It has long been recognized that the hydrocarbons representing the source of contamination in the subject matter of interest, can by ordinary chemical reactions be oxidized to harmless constituents. In principle, all such hydrocarbons can under proper conditions be oxidized to harmless end products, such as water and carbon dioxide. To date, practical methodology to achieve such results, however, have not been widely adopted. Among the strong oxidizing agents which in principle could serve these purposes is hydrogen peroxide, a composition which is readily available and at reasonable cost. Some efforts have indeed been made to utilize this oxidizing agent for these purposes. In Brown et al., U.S. Pat. No. 4,591,443, for example, an aqueous solution containing hydrogen peroxide, together with a compound for controlling the mobility of the aqueous solution by modifying the viscosity or other flow properties, is introduced into a permeable subterranean formation. It is not contemplated that the groundwater can be treated directly in this disclosure.
Forte et al., U.S. Pat. No. 4,167,973, discloses the use of strong oxidizing agents, which can include hydrogen peroxide, for treating contaminated water and the like which has been withdrawn from an underground source and is thereupon treated in a mixing device. The methodology is therefore of the pump and treat system type, and the treatment of the groundwater is not in situ.
Other patents of interest include U.S. Pat. Nos. 4,927,293 to Campbell, and 4,978,508 to Hansen et al.
Among the other deficiencies of the prior art, is the failure to define a system wherein a strong oxidizing agent such as hydrogen peroxide may be directly injected into groundwater in a manner such that it can react in situ with the hydrocarbon contaminants present in same, while at the same time providing techniques to assure the efficacy of the said method.
Pursuant to the foregoing it may be regarded as an object of the present invention to provide a method and system which enable economical, effective and rapid treatment of groundwater contaminated with hydrocarbons, so as to destroy the said hydrocarbons or reduce same to a level below that which is considered detrimental to human use.
It is a further object of the present invention to provide a method and apparatus of the foregoing character, which utilizes safe and readily available treatment chemicals, and which moreover results in output products which are harmless and safe.
It is a still further object of the invention to provide a method and apparatus which can be practiced with use of relatively simple equipment, and by relatively unskilled personnel.